1. Technical Field
The present invention relates to a wavelength tuning apparatus and method, and more particularly, to a wavelength tuning apparatus and method which can maintain highest efficiency with a single angle manipulation without changing a position of input/output light.
2. Background Art
The development of optics influences various industry fields and a wide range of next generation technologies from micromachining to high-speed communications are based on the optics. Particularly, optics applied to industrial and medical technologies such as a technique for reforming or micromachining a surface using a laser light having high straightness, a technique for separating a particular cell or a medical mass, a technique for reproducing data using optical media, high speed communications using total reflection of optical fibers, a microscope technology for recognizing a construction of a nano-size three-dimensional sample, and the like has become more important.
General laser optics mostly uses a single wavelength. However, as the demand for applications using various wavelengths increases, wavelength tuning laser optical devices that can tune wavelengths have been introduced to significantly increase a band of communications, analyze various samples, or select such a wavelength to provide optimal characteristics from among a wide range of wavelengths.
A wavelength tuning laser applying a technique for tuning a wavelength of a laser beam has a different construction according to purposes. However, a wavelength tuning laser generally applicable to various optical applications selects and outputs a desired wavelength by controlling a diffraction angle of a laser light source having a predetermined wavelength band.
FIG. 1 is a view illustrating a construction of a wavelength tuning apparatus applying a Littrow cavity that is well known. Here, the cavity represents a construction used for optical resonance including a diffraction grating, a mirror, a lens, etc., and is generally called an optical cavity.
As shown in FIG. 1, a laser light generated through a laser diode 1 becomes a parallel light through a collimator lens 2 and is incident on a reflective diffraction grating 3. The incident light is diffracted at a specific angle according to a construction of the reflective diffraction gratings 3 to be reflected from the mirror 4.
In this construction, a wavelength can be selected by controlling an angle of the diffraction grating 3, and a light path is changed according to the selected wavelength. Therefore, in order to fix the light path, complex operations such as controlling a position of the incident light or the mirror 4 are needed. In addition, an effective profile according to the diffraction angle of the incident light is different according to wavelengths, so that maintaining highest efficiency at all wavelengths is difficult. In addition, a reflective diffraction grating has absolutely low diffraction efficiency. Accordingly, diffraction efficiency of this construction is absolutely low since the reflective diffraction grating 3 is used in this construction. Therefore, when the wavelength tuning laser apparatus is implemented, a size of the apparatus is large, and maintaining the position and the path of the light is difficult. Therefore, there are problems in that high costs and a large size are needed and precision is low.
FIG. 2 is a view illustrating a construction of a wavelength tuning apparatus applying a Littman cavity. Referring to FIG. 2, a laser light generated through a laser diode 11 becomes a parallel light through a collimator lens 12 and is diffracted at a diffraction angle by a reflective diffraction grating 13. The diffracted light is reflected from a mirror 14 and incident on the reflective diffraction grating 13 again to be diffracted at a specific angle.
In this construction, a wavelength can be selected by controlling an angle of the mirror 14. Since a position of the diffraction grating 13 for reflection is fixed, there are advantages in that a position of the incident light and a path of an output light are not changed. However, this construction has a very low efficiency since not only it reflects a plurality of beams using the diffraction grating 13 which cannot reflect 100% of input light but also reflection efficiency that is changed according to wavelengths cannot be compensated. Accordingly, a range of wavelengths that can be selected is decreased. Specifically, a large number of laser diodes of which wavelength regions may overlap are needed to provide a wide range of wavelengths, so that costs are increased. In addition, a period for replacing a laser diode to select a wavelength is decreased, so that an operation time is increased. In addition, a light path is limited by the reflective diffraction grating 13 whose position is fixed, so that the selection of light path is limited. Therefore, in order to solve the limitation, additional mirror structures are needed, and a size thereof increases.
Therefore, there is a rapidly increasing need for a wavelength tuning apparatus and method in which a light path can be freely designed, the light path is not changed according to the selected wavelength, output efficiency and precision of wavelength selection are high, control needed for wavelength selection is simple, and a size thereof is small.